In order to increase the security of electronic documents against manipulation, customary measures can be implemented at the document level, such as, for instance, the provision of additional security layers that are intended to make external access more difficult. At the semiconductor level, in addition, secure chips can be used and even the software that runs thereon can be designed from the standpoint of security.
Furthermore, user-supported security features can be used on chip cards, wherein here a chip card can be regarded as an exemplary embodiment of an electronic document and/or of a proof of identity. In this regard, chip cards may include alphanumeric displays which, in interaction with the chip integrated in the chip card, can represent character sequences which can ultimately be used for authorizing activities such as accesses to buildings or cash payments. In one concrete example, a random secret number could be displayed on a display of the chip card, which the user of the chip card can use to identify himself/herself as authorized person in a process, for example taking out money at an automatic teller machine. In this case, the required energy for operating the display and further electronic components within the chip card can be drawn from a communication field in the form of a magnetic field of the automatic teller machine as reader.
Only designs in which the chip and the display element (for example an LCD display) constitute separate components, and chips which include integrated LED elements are known at the present time. However, the associated connection system between the chip incorporated in the chip card and the display element constitutes a potential target for manipulations. In this regard, a potential attacker could intervene in the signal path, for instance, in order to constrain an incorrect representation on the display element and to intercept the authentic identification characters in the process. Moreover, the required connection system causes an increased assembly outlay at the chip card level and entails the risk of failures of the overall system, for instance on account of cable- or line-break-governed interruptions at the connection system.
The patent application DE 10 2008 041 306 A1 describes a chip card including an integrated circuit and a conversion region arranged above the integrated circuit. The integrated circuit includes transmitting means for transmitting radiation to the conversion region and receiving means for receiving the converted radiation from the conversion region. Said chip card is an RFID chip card.
The patent application DE 10 2010 020 460 A1 describes a valuable document in the form of a chip card including an integrated RFID circuit including sensor elements and a light emitting element. However, for communication with the outside world, the integrated RFID circuit is coupled to an antenna arranged within the chip card by electrical and thus wear-susceptible interfaces.